This invention relates to an improved retiming system for pulse coded data and, more particularly, to an improved synchronization system for extracting the clock signals and retiming the data using the extracted clock.
In data transmission systems wherein the data is in pulse-code-modulated form, it is customary to include repeaters in the system by which the data is reshaped, amplified and retimed. The retiming is generally accomplished by extracting the clock pulses from the incoming coded data. The extracted clock signal is filtered by a narrow band-width filter to reduce timing distortions. The extracted and filtered clock signal is then used to sample the original coded data and thus produce retimed serial PCM data. It is desirable to sample the coded data exactly midway between pulse transitions so as to allow the maximum distortion in the data signal without causing sampling errors. This is difficult to accomplish at high data rates due to manufacturing tolerances of the associated circuitry, and variations in these circuits with temperature changes, power supply drift and aging.
This invention applies the unique properties of a surface acoustic wave filter in a novel way to improve the sampling synchronization of a PCM retiming system. The arrangement can be fabricated by utilizing reliable low cost large scale integration techniques.